provided by Stefen McCone

Chemical formula=C6H8O7
Too much Vitamin C (citric acid) can cause skin irritation.
The monohydrate can be changed to anhydrous by heating it above 74˚ C.
Citric Acid also dissolves in anhydrous (absolute ethanol) at 15˚ C.
most foods that contain Cirtic Acid are citric fruits (duh)
Anhydrous form crystallizes in hot water.
Monohydrate form crystallizes in cold water.
It's rare to find someone who is allergic to it, so the most that can happen could be a stomach problem.

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(Source of Citric Acid Images)